We report the results of a two-step two-dimensional (2D) diffusion study by scanning capacitance microscopy (SCM) and 2D SUPREM IV process simulation. A quantitative 2D dopant profile of a gate-like structure is measured with the SCM on a cross-sectioned polished silicon wafer. The gate-like structures consist of heavily implanted n+ regions separated by a lighter doped n-type region underneath 0.56 μm gates. The SCM is operated in the constant-change-in-capacitance mode. The 2D SCM data are converted to dopant density through a physical model of the SCM/silicon interaction. This profile has been directly compared with 2D SUPREM IV process simulation and used to calibrate the simulation parameters. The sample is then further subjected to an additional diffusion in a furnace for 80 min at 1000 °C. The SCM measurement is repeated on the diffused sample. This final 2D dopant profile is compared with a SUPREM IV process simulation tuned to fit the earlier profile with no change in the parameters except the temperature and time for the additional diffusion. Our results indicate that there is still a significant disagreement between the two profiles in the lateral direction. SUPREM IV simulation considerably underestimates the diffusion under the gate region. © 1998 American Institute of Physics.